1. Field of the Invention
The invention relates to a pole ring, particularly for d.c. motors. Further, the invention relates to an electric motor with a pole ring according to the invention. This motor is particularly suitable for controlling throttle, tumble valves and the like.
2. Discussion of the Background Art
A plurality of electric motors is used in motor vehicles. Particularly electric motors which are used, for example, for the control of valves such as throttle or tumble valves in the region of the internal combustion engine of the motor are often subject to high temperature variations. When using such electric motors in large temperature ranges, it has to be ensured that the pole ring of the electric motor is securely fixed in the entire temperature range. Even a slight turning or slipping of the pole ring may lead to a variation of the course of the magnetic field lines and thus to an impairment of the motor characteristics.
It is known to configure pole rings in a slitted manner, i.e., to provide them with a longitudinal slit to be able to compress the pole ring upon mounting, i.e., upon insertion into the motor housing. After mounting, a pole ring slitted in this manner effects a sufficient surface pressure to be securely fixed in the housing even with relatively large temperature variations. Slitted pole rings, however, are disadvantageous in that the course of the magnetic field lines is impaired by the slit. Further, mounting such pole rings that have to be compressed upon insertion into the housing is troublesome.